Invisible Particles Research Articles

Measuring properties of a dark photon from semi-invisible decay of the Higgs boson

Considerable efforts have been dedicated to discovering a dark photon via the decay of the Higgs boson to a photon and an invisible particle. A subject that is still mostly unexplored is which properties of the dark photon could be measured at the LHC if an excess were to be found in this channel and whether we could determine if this signal is indeed that of a dark photon. In this paper, we seek to address some of these questions for two Higgs production channels: gluon-fusion and Z-associated. First, prospects are presented for the upper limit on the mass of a massless dark photon and for the uncertainty on the mass of a massive dark photon. Second, we study the feasibility of distinguishing this signal from that of the Higgs decaying to a gravitino and a neutralino that decays to a photon and another gravitino. Finally, the complementary possibility of observing the decay of the Higgs to a dark photon and a Z boson is studied.

Probing invisible vector meson decays with the NA64 and LDMX experiments

Electron beam fixed target experiments such as NA64 and LDMX use missing energy-momentum to detect the production of dark matter and other long-lived states. The most studied production mechanism is dark Bremsstrahlung through a vector mediator. In this work, we explore a complementary source of missing energy-momentum signals: Bremsstrahlung photons can convert to hard vector mesons in exclusive photoproduction processes, which then decay to dark matter or other invisible particles, such as neutrinos. We find that existing NA64 data can improve the leading constraints on invisible light vector meson decays, while a future run of LDMX could improve them by up to 5 orders of magnitude. For the examples of a dark photon and a $U(1{)}_{B}$ gauge boson mediator, accounting for meson decays substantially enhances these experiments' sensitivity, especially to thermal relic dark matter of mass ${m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}0.1\text{ }\text{ }\mathrm{GeV}$.

Observation of electroweak production of two jets in association with an isolated photon and missing transverse momentum, and search for a Higgs boson decaying into invisible particles at 13\xa0text {TeV} with the ATLAS detector

This paper presents a measurement of the electroweak production of two jets in association with a Zgamma pair, with the Z boson decaying into two neutrinos. It also presents a search for invisible or partially invisible decays of a Higgs boson with a mass of 125 text {GeV} produced through vector-boson fusion with a photon in the final state. These results use data from LHC proton–proton collisions at sqrt{s} = 13 text {TeV} collected with the ATLAS detector and corresponding to an integrated luminosity of 139 hbox {fb}^{-1}. The event signature, shared by all benchmark processes considered for the measurements and searches, is characterized by a significant amount of unbalanced transverse momentum and a photon in the final state, in addition to a pair of forward jets. Electroweak Zgamma production in association with two jets is observed in this final state with a significance of 5.2 (5.1 expected) standard deviations. The measured fiducial cross-section for this process is 1.31pm 0.29 fb. An observed (expected) upper limit of 0.37 (0.34^{+0.15}_{-0.10}) at 95% confidence level is set on the branching ratio of a 125 text {GeV} Higgs boson to invisible particles, assuming the Standard Model production cross-section. The signature is also interpreted in the context of decays of a Higgs boson into a photon and a dark photon. An observed (expected) 95% CL upper limit on the branching ratio for this decay is set at 0.018 (0.017^{+0.007}_{-0.005}), assuming the Standard Model production cross-section for a 125 text {GeV} Higgs boson.

Unstable cosmic neutrino capture

Future direct observations of the Cosmic Neutrino Background (CνB) have the potential to explore a neutrino lifetime, especially in the region of the age of the universe, t0 = 4.35 × 1017 s. We forecast constraints on neutrino decay via capture of the CνB on tritium, with emphasis on the PTOLEMY-type experiment. In addition, in some cases of invisible neutrino decay into lighter neutrinos in the Standard Model and invisible particles, we can constrain not only the neutrino lifetime but also the masses of the invisible particles. For this purpose, we also formulate the energy spectra of the lighter neutrinos produced by 2-body and 3-body decays, and those of the electrons emitted in the process of the detection of the lighter neutrinos.

The Mathematical Anti-atomism of Plato’s Timaeus

In Plato’s eponymous dialogue, Timaeus, the main character presents the universe as an (almost) perfect sphere filled by tiny, invisible particles having the form of four regular polyhedrons. At first glance, such a construction may seem close to an atomistic theory. However, one does not find any text in Antiquity that links Timaeus’ cosmology to the atomists, while Aristotle opposes clearly Plato to the latter. Nevertheless, Plato is commonly presented in contemporary literature as some sort of atomist, sometimes as supporting a form of so-called ‘mathematical atomism’. However, the term ‘atomism’ is rarely defined when applied to Plato. Since it covers many different theories, it seems that this term has almost as different meanings as different authors. The purpose of this article is to consider whether it is correct to connect Timaeus’ cosmology to some kind of ‘atomism’, however this term may be understood. Its purpose is double: to obtain a better understanding of the cosmology of the Timaeus, and to consider the different modern ‘atomistic’ interpretations of this cosmology. In short, we would like to show that such a claim, in any form whatsoever, is misleading, an impediment to the understanding of the dialogue, and more generally of Plato’s philosophy.

Could MT2 be a singularity variable?

The algebraic singularity method is a framework for analyzing collider events with missing energy. It provides a way to draw out a set of singularity variables that can catch singular features originating from the projection of full phase space onto the observable phase space of measured particle momenta. It is a promising approach applicable to various physics processes with missing energy but still requires more studies for use in practice. Meanwhile, in the double-sided decay topology with an invisible particle on each side, the MT2 variable has been known to be a useful collider observable for measuring particle masses from missing energy events or setting signal regions of collider searches. We investigate the relation between the two different types of kinematic variables in double-sided decay topology. We find that the singularity variables contain the MT2 variable in many cases, although the former is not a strict superset of the latter.

Implication of J/ψ→(γ+)invisible for the effective field theories of neutrino and dark matter

We study the implication of $J/\psi$ decay into invisible particles for light sterile neutrino and sub-GeV dark matter (DM). The low-energy effective field theories (EFTs) are used for the description of general neutrino interactions and the Dirac fermion DM coupled to charm quark. For $J/\psi\to \gamma+{\rm invisible}$, we perform the likelihood fits for the individual neutrino and DM operators with distinct Lorentz structures and photon spectra. The limits on the decay branching fractions are obtained for different neutrino or DM scenarios and then converted to the lower bounds on the new energy scales. The most stringent bounds on the energy scale in neutrino and DM EFTs are 12.8 GeV and 11.6 GeV, respectively. The purely invisible decay $J/\psi\to {\rm invisible}$ provides complementary constraints on the effective operators. The relevant bound on the energy scale is above 100 GeV for the dipole operators. We also evaluate the limit on the DM-nucleon scattering cross section converted from $J/\psi$ data. The data of $J/\psi$ invisible decays are sensitive to the light DM mass range where the DM direct detection experiments cannot probe yet. The future Super Tau Charm Factory after one year run can push the limits down by two orders of magnitude.

Searching in 2-Dimensional mass space for final states with 2 invisible particles

A method to search for particles of unknown masses in final states with two invisible particles is presented. Searching for final states with missing energy is a challenging task usually performed in the tail of a missing energy related distribution. The search method proposed is based on a 2-Dimensional mass reconstruction of the final state with two invisible particles. Thus, a bump hunting is possible, allowing a stronger signal versus background discrimination. Parameters of the new theory can be extracted from the mass distributions, a valuable step towards understanding its true nature. The proof of principle is based on the existing SM top pairs in their dilepton final state. The method is applicable in many interesting searches at the LHC, including dark matter candidates or heavy top partners.

Particle Post – Letters from the Universe: A sound installation through cosmic muons

We humans are all in a constant correspondence with the universe. It speaks to us ever so subtly, showering us with invisible remnants of our mutual distant past, across the magnitude of space and time. Yet, in the infinitely grand scale of all things universal, one tends to neglect the infinitely small. It is this omnipresent chronicle of the universe that is humanity's most intimate connection to the everywhere and always, spoken to us through invisible particles and waves of energy resembling the smallest of postcards and parcels. Within the journey of each traveling particle there lies a piece of a common history, a memoir of a voyage spanning billions of years, connecting humans, in this very point in space and time, to the dawn of the universe. We propose that one way for humans to appreciate the wonders of the universe is through the poetics of sound, connecting humans to the universe by designing a sound installation. Receiving cosmic muons through a scintillation detector, a postbox subtly emits sound and light as a direct consequence to each particle it detects. This unheard sound of the universe is the result of a poetic and artistic transformation. It is therefore not a product of mere sonification, but rather of a meaningful translation of what humans do not, and cannot directly perceive. It is through this process that the implied aesthetics of the unobservable are being explored, as are the means by which it could be indirectly appreciated in different ways through the bodies and minds of humans. In this paper, the background, concepts, systems, and the collaborative process of creating this installation, Particle Post – Letters from the Universe are discussed. With the team consisting of sound designers, artists, and an experimental physicist, it was presented at the Ars Electronica Festival 2019 in Linz, Austria. Considering these processes and the result, future directions of this project are also suggested.

The light invisible boson in FCNC decays of B and B_c mesons

In this paper, we study the FCNC decay processes of B and B_c meson, in which one invisible particle is emitted. Both the spin-0 and spin-1 cases are considered. The model-independent effective Lagrangian is introduced to describe the coupling between the light invisible boson and quarks. The constraints of the coupling coefficients are extracted by experimental upper limits of the missing energy in B meson decays. The bounds are used to predict the upper limits of branching fractions of corresponding B_c decays, which are of the order of 10^{-6} or 10^{-5} when final meson is pseudoscalar or vector, respectively. The maximum branch ratios are achieved when m_chi approx 3.5–4 GeV, where m_chi is the mass of the invisible particle.

LEXICAL AND MORPHOLOGICAL RESEARCH SOME PLACE NAMES IN PAYARIK DISTRICT

The article provides a brief overview of the lexical and morphological study of some place names in Payarik district of Samarkand region, the history of place names, their affiliation, the structural types of place names. From the largest objects to the most invisible particles have their own names. It is impossible to exist in this world without a name. The name is necessary to distinguish things and events from each other.

The Invisible Threat: How Microplastics Endanger Corals

Coral reefs are one of the most endangered habitats due to climate change, but not enough attention has been paid to how plastic pollution affects coral reef health. Plastics are massively produced worldwide for many purposes and they degrade very slowly, breaking down into tiny, invisible particles of 5 mm or less, called microplastics. When these tiny particles reach coral reefs, they harm corals by constantly rubbing on them through the action of waves and currents. Corals may also ingest microplastics and get a false sense of “fullness,” which results in the coral not feeding on nutritious food. Within the coral, microplastics may block the gut and cause internal damage. Also, microplastics, which are already made of chemicals, can pick up pollutants and harmful microorganisms from the seawater and transfer them to the coral. A reduction of microplastics pollution is therefore urgent.

Search for K+ decays to a muon and invisible particles

The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+νX decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/c2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/c2 are reported for the first time, ranging from O(10−5) to O(10−7). An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.

Semi-annihilating Z3 dark matter for XENON1T excess

The recently reported result from XENON1T experiment indicates that there is an excess with 3.5σ significance in the electronic recoil events. Interpreted as new physics, new sources are needed to account for the electronic scattering. We show that a dark fermion ψ with mass about O(10) MeV from semi-annihilation of Z3 dark matter X and subsequent decay of a dark gauge boson Vμ may be responsible for the excess. The relevant semi-annihilation process is X+X→X‾+Vμ(→ψ+ψ‾), in which the final ψ has a box-shape energy spectrum. The fast-moving ψ can scatter with electron through an additional gauge boson that mixes with photon kinetically. The shape of the signals in this model can be consistent with the observed excess. The additional interaction with proton makes this model testable in future searches for nucleus recoil as well. Because of the lightness of invisible particle introduced, this scenario requires non-standard cosmology to accommodate the additional radiation component.

Search for \u03c00 decays to invisible particles

The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 109 tagged π0 mesons from K+ → π+π0(γ), searching for the decay of the π0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10−9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+ → π+X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

New collider searches for axionlike particles coupling to gluons

Axion-like particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global symmetries emerging in many extensions of the Standard Model. Assuming the most general effective Lagrangian up to dimension-5 operators for an ALP interacting with the SM fields, we investigate for the first time the sensitivity of the LHC13 to the ALP production in association with a di-jet. This study is focused on light ALPs which appear as invisible particles at the detector. Performing a realistic detector simulation and deploying a multivariate technique to best discriminate the signal from backgrounds, we set expected upper bounds on the ALP coupling to gluons. A comprehensive set of background processes is considered, and it is shown that this process provides significant sensitivity to the ALP-gluon coupling and the resulting bound is more stringent than those already obtained at the LHC. We also present prospects for the HE-LHC27 and FCC-hh100 and show that these future colliders are able to improve the limits from the LHC by roughly one order of magnitude.

Drawing dust

Over the last few years, I have become increasingly interested in how the material power of dust can be explored through the affective process of drawing to generate a new way of looking at the inevitable disintegration of the material world around us. This paper will discuss a body of drawings and prints that show how art and science have very different ways of investigating and communicating with the world around us. I am looking to science to provide an image, a particular view of the world, generating otherwise inaccessible information, but I then use a material art practice to incorporate things that are beyond the reach of science, things that science cannot engage with – the emotional, irrational, imaginative and historical ways in which we live. The body of work under discussion emerges from a research project undertaken in collaboration with an expert in the field of scientific imaging and analysis to examine particles of dust. The project considers dust as an overlooked and valuable material archive that can speak in a new way about human history and our material lives. Using state-of-the-art scientific technologies, I am able to make visible otherwise invisible particles of dust, the material that persists and remains, the omnipresent evidence of past existence. Key to the project is how the technological image that emerges from scientific analysis looks unlike anything we ordinarily see around us. The technology used to produce the scientific image creates something that seems distant, disconnected from our experience. It is this disconnection that drives me to use the slow pace and the tactile, material body of graphite drawing to transform the image using the eye and the hand in order to reconnect it with a more human, understandable way of knowing about the world.

Spin- 1/2 invisible particles in heavy meson decays

The flavor-changing neutral current decay processes of the $B$ and $B_c$ mesons with the final states involving spin-$1/2$ particles are investigated. By considering the background of the Standard Model where $\nu\bar\nu$ contributes the missing energy and the experimental upper bounds for the branching fractions, we get the constraints of the coupling constants of the quark-antiquark and the assumed invisible particles $\chi\bar\chi$. The constraints of the coupling constants are then used to study the similar processes of the $B_c$ meson. At some specific region of $m_\chi$, the upper limit of BR($B_c\to D_{(s)}\chi\bar\chi$) is of the order of $10^{-6}$, while for BR($B_c\to D^\ast_{(s)}\chi\bar\chi$), it is $10^{-5}$. The possibility of distinguishing $\chi$ to be a Majorana or Dirac fermion by the differential branching fractions is also discussed.

Is the Moon There If Nobody Looks: Bell Inequalities and Physical Reality

Various Bell inequalities are trivial algebraic properties satisfied by each line of particular data spreadsheets.It is surprising that their violation in some experiments, allows to speculate about the existence of nonlocal influences in Nature and to doubt the existence of the objective external physical reality. Such speculations are rooted in incorrect interpretations of quantum mechanics and in a failure of local realistic hidden variable models to reproduce quantum predictions for spin polarisation correlation experiments. These hidden variable models use counterfactual joint probability distributions of only pairwise measurable random variables to prove the inequalities. In real experiments Alice and Bob, using 4 incompatible pairs of experimental settings, estimate imperfect correlations between clicks, registered by their detectors. Clicks announce detection of photons and are coded by 1 or -1. Expectations of corresponding ,only pairwise measurable, random variables are estimated and compared with quantum predictions. These estimates violate significantly the inequalities. Since all these random variables cannot be jointly measured , a joint probability distribution of them does not exist and various Bell inequalities may not be derived. Thus it is not surprising that they are violated. Moreover,if contextual setting dependent parameters describing measuring instruments are correctly included in the description, then imperfect correlations between the clicks may be explained in a locally causal way. In this paper we review and rephrase several arguments proving that the violation of various Bell inequalities may neither justify the quantum nonlocality nor allow for doubt regarding the existence of atoms, electrons and other invisible elementary particles which are building blocks of the visible world around us including ourselves.

Photonic Inverse Design with Neural Networks: The Case of Invisibility in the Visible

Artificial intelligence is currently attracting unprecedented attention for its ability to tackle hard problems with huge datasets, which have been rendered tractable by the giant computational power and amount of training data available today. Photonic inverse design, in which one seeks to find objects of desired electromagnetic response, belongs to this class of complex problems that can greatly benefit from these ideas. In this work, artificial intelligence concepts are applied to advance the quest for invisible particles that do not perturb the background field; in particular, a fully connected neural network is proposed to address such a problem by learning the dynamics of visible-light interaction with low-scattering multilayered nanospheres. By swapping the roles between inputs and outputs, the same network can then be used for the inverse design of invisible nanoparticles, obtaining superior performance with respect to the best elements of the training set. The proposed approach can be generalized to approximate Maxwell interactions by simulating the electromagnetic response of more complicated optical configurations, and accomplish their inverse design directly, without successive iterations.